1. Field of the Invention
The present invention relates to a self-supporting tyre for vehicle wheels, comprising: a carcass structure having at least one carcass ply with end flaps in engagement with respective annular reinforcing structures which are disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other and each comprising at least one first circumferentially-inextensible annular anchoring insert; a belt structure applied to the carcass structure at a radially external position thereof; a tread band applied to the belt structure at a radially external position of same; at least one pair of sidewalls applied at laterally opposite positions to the carcass structure; at least one elastic stiffening insert incorporated into the carcass structure at least at one of said sidewalls.
The present invention also relates to a method of manufacturing a self-supporting tyre for vehicle wheels, comprising the steps of: preparing a carcass structure having at least one carcass ply provided with end flaps in engagement with respective annular reinforcing structures disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other and each comprising at least one first circumferentially-inextensible annular anchoring insert; applying a belt structure to the carcass structure at a radially external position thereof; applying a tread band to the belt structure at a radially external position of same; applying a pair of sidewalls at laterally opposite positions to the carcass structure; incorporating at least one elastic stiffening insert into the carcass structure, at least at one of said sidewalls.
2. Description of the Related Art
Tyres for vehicle wheels essentially comprise a carcass structure made up of one or more carcass plies that, in the most classic solutions, have the respective inner circumferential edges turned up around inextensible annular inserts being part of annular reinforcing structures and placed at axially opposite positions in the regions usually identified as tyre “beads”.
Applied to the carcass ply or plies, at a radially external position, is a belt structure comprising one or more belt layers radially superposed in succession. A tread band of elastomer material is radially superposed on the belt structure. The outer sides of the carcass structure are also covered with respective sidewalls made of elastomer material as well.
It is to be pointed out that, to the aims of the present invention, by the term “elastomer material” it is intended a rubber blend in its entirety, that is the assembly made up of at least one base polymer suitably amalgamated with reinforcing fillers and/or process additives of various types.
To give the tyre self-support qualities, i.e. the capacity to ensure ride over short-medium distances in the absence of inflation pressure, due to a puncture for example, one or more stiffening inserts of elastomer material are known to be integrated into the carcass structure, close to the tyre sidewalls; said inserts are usually referred to as “lunettes” and they conveniently support the vehicle load when the usual inflating pressure of the tyre is lacking.
In this connection different manufacturing solutions have been proposed, aiming at giving the tyre the required self-support features, without impairing ride comfort when the tyre is inflated. These solutions are essentially diversified as regards both the physico-chemical features of the elastomers employed in making the elastic stiffening inserts, and the number of the inserts to be provided, as well as in terms of positioning of said inserts relative to the carcass ply or plies.
Examples of these solutions that however do not ensure satisfactory results, are known from documents EP 0385192, U.S. Pat. No. 3,954,131 and GB 2053815 showing self-supporting structures comprising one lunette alone placed at each sidewall and disposed internally of the carcass ply or plies.
Good results, particularly as regards the tyre self-supporting capacity under deflated conditions, are achieved by adopting manufacturing solutions in which at least one of the elastic stiffening inserts which are present at each sidewall, is enclosed between two carcass plies forming a sort of closed container around it, as disclosed in documents GB 2087805, EP 475258 and EP 542252, for example.
The Applicant has however perceived that placing the elastic stiffening inserts in a sort of closed container defined by the carcass plies turned up around the annular anchoring structures tends to increase stiffness of the tyre sidewall too much, not only with reference to its vertical flexibility, i.e. in connection with substantially radial stresses with respect to the rotation axis of the tyre, but also with reference to its torsional responsiveness, i.e. in connection with stresses directed tangentially of the circumferential extension of the tyre itself.
By adopting particular expedients, as described in documents EP 475258 and EP 542252 in the name of the same Applicant for example, the possibility of restricting within limits, the vertical stiffness of the sidewall under running conditions with an inflated tyre are achieved. On the other hand, these technical solutions tend to make the tyre structure more complicated and heavier and are not efficient for the purpose of limiting the torsional stiffness which, as found out by the Applicant, is one of the decisive factors in terms of ride comfort, particularly at medium/high speeds. In fact, the tyre capacity of absorbing impacts transmitted by potholes or other unevennesses present in a road surface depends on the torsional stiffness of the tyre.
In accordance with the present invention it has been found that in the field of self-supporting-tyre manufacture, unexpected advantages can be reached if the elastic stiffening inserts have flaps axially overlapping the inextensible annular inserts, to ensure better anchoring of the reinforcing element to the annular structures and, through it, to the mounting rim during use at zero pressure.
In particular, it is an object of the present invention to provide a novel self-supporting tyre characterized in that said elastic stiffening insert has a radially-internal end portion disposed at least partly in axial side by side relationship against said first annular anchoring insert.
It is a further object of the invention to provide a method of manufacturing a self-supporting tyre for vehicle wheels, characterized by the fact of disposing said at least one first annular anchoring insert at a position in side by side relationship against a radially-internal end portion of the elastic stiffening insert.